Pharmacologic Modulation of the IgE or Ca2+ Ionophore A23187 Mediated Ca2+ Influx, Phospholipase Activation, and Histamine Release in Rat Basophilic Leukemia Cells

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Abstract
The stimulation of the rat basophilic leukemia cells (RBL-2H3) mediated either through the IgE receptor or by the Ca2+ ionophore A23187 results in 45Ca2+ influx, phospholipase activation, and histamine release. This study compared in parallel the effects of pharmacological agents on 45Ca2+ influx, phospholipase activation as measured by the release of [14C]-arachidonic acid, and histamine release. Microtubule-depolymerizing agents (demecolcine, colchicine, and vinblastine sulfate) did not affect 45Ca2+ influx, but blocked the IgE- or A23187-mediated [14C]-arachidonic acid and histamine release (e.g., IC50 for vinblastine sulfate = 10 nM). In contrast, a microtubule-stabilizing agent (taxol) blocked the IgE- and A23187-mediated 45Ca2+ influx and [14C]-arachidonic acid and histamine release (IC50 = 20 µM). Microfilament-disrupting agents (cytochalasin B, C, D, and E) enhanced 45Ca2+ influx and [14C]-arachidonic acid and histamine release in the same dose-dependent fashion (e.g., EC50 for cytochalasin B = 0.4 µM). Other pharmacological agents such as a metabolic inhibitor (antimycin A), calmodulin inhibitors (W-7, trifluopromazine), and protease inhibitors (TPCK and TLCK) blocked the IgE- and A23187-mediated 45Ca2+ influx and [14C]-arachidonic acid and histamine release. Therefore, the coupling of Ca2+ influx and the phospholipase activation step requires a functioning microtubule system. Other inhibitors act at sites prior to the Ca2+ influx step in the release process.